The present disclosure relates generally to fuel systems for gas turbine engines. In particular, the present disclosure relates to fuel systems utilizing fuel flow from two fuel pumps to provide combustion fuel and to operate engine actuation systems.
In conventional fuel systems, a main fuel pump is used to deliver fuel to a fuel metering valve that provides fuel directly to fuel injectors in the combustion section of a gas turbine engine. Additionally, some of the fuel flow from the main fuel pump is circulated through actuators that operate other engine or aircraft systems. Such a system is described in U.S. Pat. No. 4,487,016, which is assigned to United Technologies Corporation. In some systems, the metering valve is controlled with a servo valve-controlled torque motor that provides fuel based on engine requirements for different speeds, and servo valve-controlled actuators are used to regulate airflow to active clearance control systems based on the fuel flow. The servo valves utilize fuel flow from the main fuel pump to provide actuation. The main fuel pump needs to be sized at a minimum to provide flow to the servo valves and to the injectors at start and idle engine speed, and at a maximum to provide flow to the servo valves and to the injectors under transient engine conditions, such as during take-off. Thus, the main fuel pump must have a large capacity to accommodate the entire engine operating envelope and to provide fuel to other various aircraft systems.
More recent systems have utilized a dedicated servo pump to service the actuators in order to reduce inefficiencies of a large main fuel pump. Additionally, it is desirable to ensure that the dedicated servo pump generates enough flow and pressure to ensure operation of the actuators in the event of an engine shutdown. One dual-pump system is described in Pub. No. U.S. 2012/0234015, which is assigned to Hamilton Sundstrand Corporation. This system, however, relies on a pressure regulating valve that has multiple windows controlling multiple fuel flows with a single spool. There is a need for a more efficient and more easily controlled fuel and actuation system for gas turbine engines.